The influence of work characteristics on body mass index and waist to hip ratio in Japanese employees

A cross-sectional study on 6,676 workers consisting of 4,243 males and 2,433 females aged 20-58 yr in a metal product factory was conducted to elucidate the relationship between work characteristics, e.g. job demand/control/support, sedentary job, overtime work and shift work, and waist to hip ratio (WHR) as well as body mass index (BMI) taking alcohol consumption, smoking, exercise and other psychosocial factors such as education and marital status into account. By a stepwise multiple regression analysis, BMI was associated with shift work, marital status and sedentary job for males, and with exercise but inversely associated with education for females. WHR was also associated with shift work, alcohol consumption, marital status and sedentary job but inversely associated with exercise for males, and with sedentary job, marital status and education but inversely associated with smoking for females. These results suggest that work characteristics such as sedentary job and shift work should also be considered when trying to prevent increases in BMI and WHR.     

Markers of insulin resistance in day and shift workers aged 30-59 years

OBJECTIVES: To examine relationships between shift work and markers (metabolic abnormalities) of insulin resistance (IR). METHODS: A cross-sectional study of 2,824 day and 826 shift workers. All the subjects were male blue-collar workers aged 30-59 years. Four IR markers [(1) hypertension (systolic blood pressure >or=140 mmHg or diastolic blood pressure >or=90 mmHg or under treatment for hypertension); (2) hyperglycemia (fasting serum glucose >or=7.00 mmol/l or under treatment for diabetes); (3) hypertriglyceridemia (fasting serum triglyceride >or=1.70 mmol/l or under treatment for hyperlipidemia); (4) hypo-HDL-cholesterolemia (fasting serum HDL-cholesterol <1.04 mmol/l)] were checked. Subsequently, IR syndrome, a cluster of IR markers, was expediently diagnosed by the number (N) of IR markers found in each worker. N>or=1, N>or=2 or N>or=3 was used as a cutpoint for the diagnosis. The prevalence of each IR marker and IR syndrome was compared between the two worker groups. Age, body mass index (kg/m(2)), job, drinking, smoking, and exercise were used as confounding factors. Job, work schedule and lifestyles were based on self-administered questionnaires. RESULTS: Hypertriglyceridemia (28.7% in day workers, 31.2% in shift workers) was most prevalent (4.6%), and hyperglycemia (5.4%) was least, in the four IR markers in both worker groups. Approximately half of the subjects had at least one IR marker in both groups (N>or=1; 46.0% and 46.6%, respectively). However, a full cluster of IR markers was rare in both groups (N=4; 0.2% and 0.1%, respectively). Prevalence of IR syndrome by any cutpoints increased with age in day workers, but shift workers aged 50 years or older had lower prevalence than shift workers younger than 50 years. In subjects younger than 50 years, all IR markers (except for hypo-HDL-cholesterolemia) and IR syndrome by any cutpoints were more prevalent in shift workers than in day workers. Contrariwise, in subjects aged 50 years or older, lower prevalence of all IR markers and IR syndrome in shift workers than in day workers was found. These results were not influenced by statistical adjustments for the confounding factors by multiple logistic regression analysis. CONCLUSIONS: Shift work may be associated with IR syndrome in workers younger than 50 years. These relations may be underestimated mainly by broad definition of shift work and healthy-worker effects.     

A retrospective cohort study of shift work and risk of cancer-specific mortality in German male chemical workers

Objectives

Human evidence of carcinogenicity concerning shift work is inconsistent. In a previous study, we observed no elevated risk of total mortality in shift workers followed up until the end of 2006. The present study aimed to investigate cancer-specific mortality, relative to shift work.

Methods

The cohort consisted of male production workers (14,038 shift work and 17,105 day work), employed at BASF Ludwigshafen for at least 1 year between 1995 and 2005. Vital status was followed from 2000 to 2009. Cause-specific mortality was obtained from death certificates. Exposure to shift work was measured both as a dichotomous and continuous variable. While lifetime job history was not available, job duration in the company was derived from personal data, which was then categorized at the quartiles. Cox proportional hazard model was used to adjust for potential confounders, in which job duration was treated as a time-dependent covariate.

Results

Between 2000 and 2009, there were 513 and 549 deaths among rotating shift and day work employees, respectively. Risks of total and cancer-specific mortalities were marginally lower among shift workers when taking age at entry and job level into consideration and were statistically significantly lower when cigarette smoking, alcohol intake, job duration, and chronic disease prevalence at entry to follow-up were included as explanatory factors. With respect to mortality risks in relation to exposure duration, no increased risks were found in any of the exposure groups after full adjustment and there was no apparent trend suggesting an exposure–response relation with duration of shift work.

Conclusions

The present analysis extends and confirms our previous finding of no excess risk of mortality associated with work in the shift system employed at BASF Ludwigshafen. More specifically, there is also no indication of an increased risk of mortality due to cancer.     

Sleep-disordered breathing and hypertension in Japanese steel workers

Sleep-disordered breathing (SDB) is the major determinants of hypertension. Recent studies indicated sleep duration, in addition to shift work, were also associated with hypertension. But very little attention has been paid to these two factors when looking at the effects of SDB on blood pressure. We conducted the present study to evaluate the relationship between SDB and hypertension adjusting for sleep duration and shift work in a sample of Japanese steel workers. In this cross-sectional study, we measured blood pressure and oxygen desaturations index (ODI) by nocturnal pulse oximetry of 249 male workers aged 20 to 65 yr. SDB was defined by 3%ODI level of 15 or more events per hour. Logistic regression analyses were performed to estimate the associations of SDB with hypertension after adjustment for age, body mass index, alcohol intake, smoking, usual sleep duration, shift work, and occupation. The prevalence of SDB was 18.1%. The adjusted odds ratio of hypertension for high (> or =15) vs. low (<15) category of 3%ODI level was 2.86 (95% confidence interval, 1.23-6.66). The significant association between SDB and hypertension suggests that screening for SDB among steel workers is useful for prevention of hypertension.     

The relationship between shift work and the onset of hypertension in male Japanese workers

We assessed the effect of shift work on the onset of hypertension. The design of this study was that of a cohort study from 1991-2001. In sum, 5338 workers comprised this cohort. The event was the onset of hypertension (systolic blood pressure >or=140 mm Hg and/or diastolic blood pressure >or=90 mm Hg and/or medication). Pooled logistic regression analysis was performed, including job schedule type, age, body mass index, lifestyle, and the results of blood chemistries as covariates. The odds ratio of the onset of hypertension in shift workers for daytime workers was 1.10 and significant. Our study revealed that shift work independently affected the onset of hypertension, and suggested that shift work is a risk factor for the onset of hypertension.     

Relationship between two job stress models and coronary risk factors among Japanese part-time female employees of a retail company

The objective of this study was to explore the associations between two major job stress models (job strain and effort-reward imbalance) and coronary heart disease (CHD) risk factors (blood pressure; total, high- (HDL) and low-density lipoprotein (LDL) cholesterol; and triglycerides) in Japanese part-time female employees of a retail company. The study population was either 35 yr old or between 40 and 63 yr old. Data collection was carried out in 2002; a total of 1,401 subjects participated in a medical examination and completed a questionnaire. After adjusting for other covariates (age, relative weight, tobacco use, alcohol consumption, lack of exercise, education, marital status, history of child bearing, medical treatment for disease, and occupation), a significant association was found between the effort-reward imbalance, a "high-cost and low-gain" condition at work, and a high prevalence of low HDL cholesterol (Odds ratio=4.4). A weak but unexpected association was found between job strain and low prevalence of low HDL cholesterol. In explanatory analysis with individual components of the two models, associations were evident between high extrinsic effort and high prevalence of low HDL cholesterol and low prevalence of high triglyceride, high job control and low prevalence of high systolic blood pressure, and high job demands and low prevalence of high systolic and diastolic blood pressure. In this cross-sectional study of Japanese part-time working women, a significant association was found between effort-reward imbalance and unfavorable HDL cholesterol profiles. The findings did not support the hypothesis that job strain is associated with CHD risk factors.     

Three-shift system increases job-related stress in Japanese workers

We assessed the relationship between shift work and job stress. The target subjects were 4,962 male workers (3,078 day workers and 1,884 shift workers) aged 18 to 60 yr who work in a Japanese steel company. We used the "Brief Job Stress Questionnaire", which was developed by a research group organized by the Japanese Ministry of Labour. We evaluated the effect of shift work on job stress using logistic regression analysis including age, lifestyle factors, work conditions, marital status, and living arrangements in the model. Job schedule type was significantly associated with job control, with an odds ratio of 2.22 for shift workers compared to day workers. The logistic regression analysis revealed that the odd ratios for having one or more stressor items in an unfavorable condition were significantly higher for shift workers compared to day workers. Increase in the amount of overtime and decrease in the number of holidays led to a significant deterioration in job stress. Our study reveals that the 3-shift system of employment increases work-related stress, and that job control is low among shift workers. To reduce job stress in this occupational population, a reduction in the amount of overtime and an increase in the number of holidays seem to be useful interventions.     

Relationships of working conditions and individual characteristics to occupational injuries: a case-control study in coal miners

This study assessed the relationship of age, poor perception of working condition, poor safety environment, poor management and supervision, risk-taking behavior, emotional instability, negative job involvement, job dissatisfaction, job stress, and poor safety performance of workers to occupational injuries. This case-control study was conducted on 202 male coal miners with at least one occupational injury during a five-year period and 202 male controls with no occupational injury, matched on the job. A standardized questionnaire administered by individual interviewers was used. Data were analysed by the logistic regression method. For all workers combined, the factors with significant adjusted odds ratios (ORs) found were: 30-45 and >45 yr age groups (OR vs. <30 yr age group: 1.80, 95% CI 1.02-3.17 and 2.59, 1.38-4.85 respectively), poor perception of working conditions (1.61, CI 1.00-3.18), emotional instability (2.33, 1.04-5.22), job stress (1.83, 1.00-3.46) and poor safety performance of workers (3.10, 1.45-6.63). No significant interaction was found between these risk factors and the job. It was concluded that older age, poor perception of work conditions, poor work environment, and human behavioral factors played significant roles in occupational injuries. This information would help in implementing preventive programs to improve working conditions and management quality and to help the workers to develop positive psychological traits, but workers with negative traits such as emotional instability and older workers should be employed in less demanding jobs.     

邢台市男性煤炭工人睡眠与肾功能异常的关系

  目的  探讨邢台市男性煤炭工人睡眠与肾功能异常之间的关系,为男性煤炭工人的肾脏疾病防治提供理论依据。  方法  采用现况研究,收集河北省邢台市2家煤炭公司的3 774名井下男性煤炭工人的问卷和血生化指标等信息。采用多因素Logistic回归分析模型分析倒班、睡眠时长和失眠或睡眠评分与肾功能异常的关系。  结果  男性工人的肾功能异常检出率为5.3%,倒班、睡眠时长≤5 h、失眠的工人占比分别为63.2%、4.0%及10.0%。调整年龄、睡眠时长、倒班状态、失眠等因素后,多因素Logistic回归分析模型分析结果显示,现在倒班(OR=1.557, 95% CI: 1.078~2.250, P=0.018)、睡眠时长≤5 h(OR=1.886, 95% CI: 1.005~3.540, P=0.048)、有睡眠问题组(OR=1.810, 95% CI: 1.286~2.546, P=0.001)与肾功能异常的联系减弱,失眠与肾功能异常联系无统计学意义(P=0.279)。根据倒班状态进行分层分析,调整相关混杂因素后发现,现在倒班的煤炭工人肾功能异常患病风险随睡眠评分等级的增加而增加(P_趋势=0.001)。  结论  每天睡眠时长≤5 h、现在倒班与男性煤炭工人肾功能异常独立相关,且睡眠问题越严重,肾功能异常的患病风险越高。     

Investigation of postural hypotension due to static prolonged standing in female workers.

The "Just-in-Time system" improves productivity and efficiency through cost reduction while it makes workers work in a standing posture. The aim of this study was to investigate the prevalence of postural hypotension in females during prolonged standing work, and to discuss preventive methods. Twelve female static standing workers (mean age+/-standard deviation; 32+/-14 yr old), 6 male static standing workers (30+/-4 yr old), 10 female walking workers (27+/-7 yr old) and 9 female desk workers (31+/-5 yr old) in a certain telecommunications equipment manufacturing factory agreed to participate in this study. All participants received an interview with an occupational physician, and performed the standing up test before working and ambulatory blood pressure monitoring (ABPM) while working. Although the blood pressure of the standing up test did not differ among the groups, mean pulse rates on standing up significantly increased in every group. Hypotension rates in the female standing workers' group by ABPM were 9 persons of 12 participants (75%) for systolic blood pressure (SBP), and were 11 persons of 12 participants (92%) for diastolic blood pressure (DBP). There were significantly higher than those in the female desk workers' group, none of 9 participants (0%) for SBP and 2 of 9 participants (22%) for DBP. The hypotension rates both male standing and female walking worker groups did not differ. Because all 8 workers who were found to have postural hypotension by the standing up test had decreased SBP and/or DBP by ABPM, it is suggested that persons at high risk of postural hypotension during standing work could be screened by the standing up test. The mechanism of postural hypotension may be a decrease of venous return due to leg swelling, and neurocardiogenic or vasovagal response. Preventing the congestion of the lower limbs by walking, managing standing time and wearing elastic hose to keep the amount of the venous return could prevent postural hypotension during prolonged standing work.     

Metabolic disturbances in male workers with rotating three-shift work. Results of the WOLF study

OBJECTIVES: The aim of the present study was to investigate the relationship between important metabolic risk factors for coronary heart disease (CHD) and type 2 diabetes in shift workers and day workers. METHODS: Cross-sectional data from a sub-population in the WOLF study consisting of 665 day workers and 659 three-shift workers in two plants were analysed. RESULTS: A higher proportion of shift workers than day workers had high triglyceride levels (> or =1.7 mmol/l), low levels of HDL-cholesterol (<0.9 mmol/l) and abdominal obesity (waist/hip ratio>0.9). The risk of low HDL-cholesterol was doubled in shift workers, (odds ratio (OR): 2.02, 95% confidence interval (95% CI): 1.24-3.28) after being adjusted for age, socio-economic factors, physical activity, current smoking, social support and job strain. High levels of triglycerides were also significantly associated with shift work (OR: 1.40, 95% CI: 1.08-1.83). The OR for abdominal obesity was 1.19, (95% CI: 0.92-1.56). The prevalence of hyperglycaemia (serum glucose > or =7.0 mmol/l) was similar in day and shift workers. No significant interaction was seen between shift work and abdominal obesity with regard to the associations with triglycerides and HDL-cholesterol. CONCLUSIONS: We found a significant association between shift work and lipid disturbances (i.e. low HDL-cholesterol and high triglyceride levels). We did not find any association with hyperglycaemia.     

Cardiovascular dysfunction due to shift work.

Electrocardiographic, biochemical, and physical data obtained from 237 shift and 115 day workers without any obvious disorders were assessed to clarify the impact of shift work on cardiovascular functions. The heart-rate corrected QT interval (QTc) was significantly longer in the shift workers than in the day workers. However, blood pressure, working duration, and biochemical and other data were comparable between the two work groups. When multiple regression analysis was used, shift/day work was significantly related to the QTc in all of the workers. The adjusted odds ratio of shift work to the prolonged QTc (> or = 440 ms1/2) was 8.15. The prolonged QTc has been thought to contribute to an increased risk of cardiac death. These findings, therefore, suggest that the increased risk for cardiovascular mortality in shift workers may be attributable to prolongation of the QTc.     

Shift work and risk of non-cancer mortality in a cohort of German male chemical workers

Objectives

Shift work is widely considered to be a health risk. In a previous study, we observed no elevated risk of total mortality in BASF shift workers followed up until the end of 2006. The present study aims to investigate non-cancer mortality, especially mortality caused by ischaemic heart disease (IHD), relative to shift work.

Methods

The cohort consisted of 14,038 male shift and 17,105 male day workers from manufacturing plants, who were employed for at least 1 year between 1995 and 2005. Vital status was followed from 2000 to 2009. Cause-specific mortality was obtained from death certificates. Non-cancer mortality as well as mortality specific to diagnoses from I20.0 to I25.9 according to International Classification of Disease version 10 was compared between the two working-time systems. To estimate the impact of shift work on the outcome of interest, Cox proportional hazard model was used to adjust for potential confounders such as age, smoking, alcohol consumption, job level, and disease status at baseline. The effect estimates were then given as hazard ratio (HR) with 95 % confidence interval (CI).

Results

Between 2000 and 2009, a total of 1,062 deaths occurred in the cohort: 513 (3.6 %) in shift and 549 (3.2 %) in day workers. Among them were 122 deaths resulting from IHD, 55 (0.39 %) and 67 (0.39 %), respectively. After adjustment for age at entry and job level, no increased risk of non-cancer mortality (HR 0.94; 95 % CI 0.77–1.15) as well as of IHD-caused mortality was found among shift workers (HR 0.77; 95 % CI 0.52–1.14). The risk estimates were robust after further adjustment for more factors in all models and consistently tended to be in favour of shift workers. Considering the duration of exposure to shift, no dose–response relationship was found.

Conclusion

The present analysis does not find strong evidence for an increased mortality risk due to non-cancer disease and, more specifically, IHD-caused mortality associated with this shift system. Initial selection based on health criteria as well as ongoing health surveillance and health promotion is likely to have contributed to this result. Shift work over 34 years may lead to a loss of this initial selection advantage over time, but the respective risk estimates lacked statistical precision.     

Shiftwork and mortality from ischaemic heart disease.

OBJECTIVES: To investigate the relation between shift work and death from ischaemic heart disease (IHD). METHODS: A nested case-control approach was used. The cohort comprised male manual workers who joined an industrial company aged 50 years or under between 1 January 1950 and 31 December 1992 and worked there for at least one month. Cases were 467 cohort members who died during the same period aged 75 years or under, with ischaemic heart disease (IHD) (international classification of diseases (ICD) 410-414) coded from the death certificate. For each case a control worker was chosen, who joined the company at the same age and in the same period but who survived the case. Work status (shift work or day work) was assigned to cases for their entire employment and to controls for that part of their employment which preceded the matching case's death. The main source of information was historical personnel records containing pay codes which differed for day work and shift work. Information on weight, height, blood pressure, and smoking from a pre-employment medical was available. RESULTS: Two thirds of subjects had been employed for at least one month as shift workers and there was evidence that they had slightly better health at recruitment than day workers. The odds ratio for shift workers during the period starting 10 years after shift work began, and after adjustment for height, body mass index, blood pressure, smoking, duration of employment, and job status (skilled or unskilled) was 0.90 (90% confidence interval (90% CI): 0.68-1.21). There was no relation between risk of IHD death, and duration of shift work, but there was evidence of a reduced risk when actively employed as a shift worker, together with an increased risk in the first five years after leaving shift work to do day work. CONCLUSIONS: Shift work did not increase the risk of death from ischaemic heart disease in this study. Those workers with poorer cardiovascular health may be under represented in groups with longer shift work experience because of health related selection out of shift work.     

Job characteristics and blood coagulation factors in Korean male workers

This study examined the possible relationship between Karasek's job strain model and blood coagulation factors VII and VIII as risk factors for cardiovascular disease in Korean male workers. Based on the postulation of the model, we invited 160 male workers (40 people each subgroup) using a stratified sampling from the base population (n = 1071). In univariate analyses, decision latitude was negatively related to blood coagulation factors VII and VIII. Work demand was positively related to coagulation factor VIII, but not to factor VII. Hierarchical multiple regression analyses showed that job strain was associated with blood coagulation factor VIII after controlling for smoking, blood pressure, total cholesterol, and HDL cholesterol. These results indicate that job characteristics may be related to blood coagulation, and contribute to the development of cardiovascular disease with other classical risk factors.     

Increased risk of coronary heart disease in Japanese blue-collar workers

The purpose of this study was to test the hypothesis that blue-collar workers have an increased risk of coronary heart disease. Subjects were 653 male (mean age, 32.6 years) and 492 female (mean age, 26.3 years) workers employed during 1993 at a computer manufacturing company. The measurements determined were body mass index (BMI), waist to hip ratio (WHR), skinfold thickness, blood pressure, grip strength, back strength, vertical jump and trunk flexion. Male blue-collar workers had significantly higher WHR (P < 0.001), systolic blood pressure (P = 0.031), grip strength (P = 0.030), and standing flexion (P = 0.038) than do white-collar workers. Female blue-collar workers had significantly higher BMI (P = 0.018), WHR (P < 0.001), and grip strength (P = 0.007). Blue-collar workers took significantly less exercise, and habitually snacked (females only), smoked and drank more alcohol (males only) than white-collar workers. In conclusion, blue-collar workers have more intra-abdominal fat than white-collar workers of either sex. The difference may be due to factors contributing to the less healthy lifestyles of blue-collar workers.     

Evaluation of the relationship between subclinical hypothyroidism and metabolic syndrome components among workers

Objectives

Both hyperthyroidism and overt hypothyroidism are associated with increased prevalence of metabolic syndrome and its components, while data on subclinical hypothyroidism is currently limited especially in working populations. The aim of this study was to examine the association between subclinical hypothyroidism and metabolic syndrome components in workers; and to evaluate whether there are differences by sex and occupation.

Material and Methods

A total of 1150 university employees (male — 792, female — 358) aged 30–60 years who came for an annual medical check-up were studied. Anthropometric measurements were taken, and blood pressure, fasting plasma glucose (FPG), lipid profiles, thyroid stimulating hormone (TSH), free thyroxin (FT4) and free triiodothyronine (FT3) levels were measured.

Results

After adjustment for age and body mass index (BMI), TSH was positively associated with increased triglyceride (TG) levels (β = 0.108, p = 0.020) and FPG (β = 0.130, p = 0.006) in subclinical hypothyroid male workers. However, TSH was not associated (p > 0.05) with any component of metabolic syndrome (MS) in the euthyroid group. In females, TSH was not correlated with MS components in both euthyroid and subclinical hypothyroid groups. Furthermore, comparison by occupation showed higher TSH in subclinical hypothyroid male workers employed in administration (5.23±0.52 mU/l) than those working as academics (5.12±0.52 mU/l), which resulted in elevated systolic and diastolic blood pressure, FPG, total cholesterol, TG and high density lipoprotein cholesterol. In females, BMI, systolic and diastolic blood pressure, TG and FPG were significantly (p < 0.05) higher in subclinical hypothyroid administrators than those in academics.

Conclusions

Subclinical hypothyroidism was associated with metabolic syndrome components in male workers and not in females. Administration workers showed increased metabolic risks compared to academics. The findings suggest that the assessment of thyroid function in individuals with metabolic syndrome in the workplace may be favorable especially among men.     

Cardiovascular effects of occupational exposure to carbon disulphide

The objective of this study was to investigate the effect of occupational exposure to carbon disulphide (CS2) on the total cholesterol, blood pressure and prevalence of coronary heart disease (CHD). A cross-sectional study involving 252 viscose rayon workers and 252 age and sex matched controls was carried out. Depending on the job and specific work place, the CS2 concentrations were between 10 and 64 mg/m3. A cumulative exposure index (CS2 index) was calculated for each worker by multiplying the number of years he had held a particular job with the CS2 concentrations in that job. CHD prevalence among the exposed was higher than among the controls; the difference reaching significance only for highly exposed workers. Cholesterol levels were significantly higher in both highly and moderately exposed groups. In conclusion, the results demonstrated that occupational exposure to CS2 increases total cholesterol and the risk for CHD. While the risk for CHD is increased in workers exposed to high CS2 concentration for many years (CS2 index > or = 300), even the relatively modest exposure (CS2 < 300) may increase the serum cholesterol.     

Effect of work conditions and work environments on the formation of 8-OH-dG in nurses and non-nurse female workers

The purpose of our study was to examine the effects of job stress factors on oxidative DNA injuries among female workers. The levels of urinary 8-hydroxydeoxyguanosine (8-OH-dG) were measured along with a survey on work conditions and environments. The result showed that female workers in shift work excreted increased levels of 8-OH-dG in comparison with the result of those who were engaged in part time work (P < 0.01). Moreover, the nurses who marked higher depressive scores excreted significantly increased levels of urinary 8-OH-dG than the nurses who scored lower depressive states. The result revealed a positive correlation between 8-OH-dG levels of nurses in the 35-45 age group and the individual scores of their depressive states (r = 0.32, P < 0.05). Together, it was suggested that a heavy burden of work in addition to daily domestic roles increases urinary excretion levels of 8-OH-dG.     

Effect of shift work on body mass index and metabolic parameters

OBJECTIVES: The aim of this cohort study was to investigate the effects of shift work on changes in parameters related to metabolic disturbances. METHODS: The study population included 1529 male blue-collar workers, aged 19-49 years at baseline, working in a sash and zipper factory in Japan. The participants were divided into four groups according to the work schedule at baseline, the end point being workers doing fixed daytime work in both years (day-day), workers who changed from shift work to fixed daytime work (shift-day), workers who changed from fixed daytime work to shift work (day-shift), and workers doing shift work in both years (shift-shift). The changes in body mass index (BMI), blood pressure, serum cholesterol, and glycosylated hemoglobin A1c over a period of 10 years were compared among the groups by work schedule. RESULTS: The age-adjusted mean increase in BMI was 1.03 kg/m(2) for the day-shift workers, and it was significantly larger than that of the day-day workers and shift-day workers. The shift-shift workers showed a significantly larger increase in BMI than the day-day workers. These tendencies remained after adjustment for age and all other confounding factors, such as BMI, smoking, drinking, and leisure-time physical activity at baseline. The increase in total cholesterol tended to be higher among the shift-shift workers and the day-shift workers, but there were no significant differences. Blood pressure and hemoglobin A1c did not differ among the four groups. CONCLUSIONS: Shift work is considered to be a risk factor for excess weight. However, no significant difference in the biomarkers was found between daytime workers and shift workers.